A123 20AHr Pouch Cell Battery Build & Info Thread

Michall2008 said:
After about one minute i stop the test because the wooden suffice the bulbs was mounted on started to smoke :shock:
got to figure out how to mount those safely, any ideas ?
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loko upauraslips' disharger projetc with halgoenbulbs

There is a huge spark when i connect the 4mm bullet connectors, how do I get rid of it ?
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lookup precharge
 
izeman said:
i received my 42 cells today. packaging was quite nice. nothing to complain about.
cells don't look that nice. like being ripped out of something with pure power. at least the tabs look like that. some cells also have this funny 900mah sticker - which i don't believe.
i started measuring them. only the first cells, because if got to leave now. all of them have 3.295v. that's fine.
but now for the bad: internal resistance at that voltage measure with my icharger 206b was between 21 and 44 mOhm. that seems WAY to much - isn't? that should be below 5 mOhm afaik. can anyone confirm?
i will post pictures and detailed discharge charts asap.
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I believe the spec on these is [edited wrong, see below]. I would imagine that the margin of error on the icharger as well as some recycle cells account for it. I don't imagine that's a dealbreaker for most DIY applications by any means.
 
I believe the datasheet IR is 0,5mOhm. Certainly not 15mOhm!

My guess is the hyperion is faulty at measuring them, if not - you've got some shitty cells.
 
My bad, not sure where I found that, I just found a .2mOhm nominal spec. It would help if they actually put that in the datasheet.

0.2mOhm is impossible to measure properly without an appropriate kelvin AC meter I imagine. The leads at that point have considerable amount of I.
 
I'm afraid that the Hyperion is not so accurate measuring IR. It varies in the charge cycle and seems not to be reproducable over several charges. My 12S A123 pack seems to average 25 mohms but it is never the same after a full charge. It has gone to over 100 mohms and down to 5. Not great for actually getting a value.
otherDoc
We need something like DrBass's new toy but at over a grand it is not in my budget. I just bought some extra cells and got rid of one that appeared sub standard on D/C testing.
 
Just to put it into perspective at 5A discharge (I don't know what it actually discharges at), the ADC of the icharger would have to read ~1.5mV. Considering it has to have a ~20V range, it would have to be like a 24 bit ADC to have any hope of getting that kind of resolution, Not to mention analog electronics to back it up and 4 wire leads...
 
At least I got a reasonable discharge rate of 18.960mah at my first test. Not bad. But voltage sag was extreme. Dropped from 3.65v to 3.3v within 2.000 mah. Then stayed a while at 3.15v. Discharged to 2.4v. After decharching voltage moved up to 3.1v.
Need to find some accurate charging sheets to compare.
I'll do some more resistance testing again. At least with my lipo setup measuring was showing 2-5mohm.
 
Regarding the scorched bolt and tubing on my build, I would say it was mostly self-inflicted. There should definitely be nothing flamable in the pack as mentioned above. I intended the masonite as a template for the final polyethylene end pieces. The bolt was zinc coated steel and I only hand tightened the nut securing the terminal ring to the bolt, so there may also have been some arcing. I'm still waiting on parts from HobbyKing before the final build of my pack.

I was also making a crude attempt at a load test of the pack using the watt meter on the bike by intentionally "draining/abusing" the battery. I did no pedaling, lots of starts from dead stop and climbing up some serious inclines. I intentionally went up a roughly 30 degree slope about 3500 feet long at about 8mph drawing almost 30amps the entire distance. I knew the wires would get hot since this also happens with my SLA battery setup. I just didn't think it would get hot enough to heat up the nut and bolt to melt the tape and tubing. The electrical tape was the cheap stuff from Harbor Freight, not the better 3M tape. Better to find these problems now before my final build.

So at least my testing illustrated that there are heat issues to be concerned about. Given that these packs are duct taped or encased in some type of covering or container with no real air circulation, builders need to be aware of the thermal considerations depending on their application.

I had fun with this build, but if I had to do it over again, I would seriously consider the new OSN kit. However, I am still waiting on some feedback on that kit from other forum members. I figure I spent about $25 in equivalent hardware costs to the $40 (not including shipping) for the OSN kit and no drilling holes in the tabs. Nancy at OSN also claims that they tested their kit with 100amp loads, way more than the 30amps I'm using.

By the way, on a level asphalt road, my e-bike runs at over 30mph at 30amps.
 
i did not see a separate nut that secured the lug to the end of the bolt.

you should not use steel as a conductor. use brass screws. use brass nut and locknut to clamp the lug to the end of the screw if you cannot solder it. then you can insert it through the hardboard. using plastic is not gonna make any difference just more money.

if you want electrical isolation, use a nylon insulating washer under the nuts on each side of the masonite, and the sleeve around the screw shaft in the middle can be heatshrink tubing.

if you run long metal screws through the pack on the end where the tabs are exposed, you should use insulating sleeves on them too.
 
izeman said:
At least I got a reasonable discharge rate of 18.960mah at my first test. Not bad. But voltage sag was extreme. Dropped from 3.65v to 3.3v within 2.000 mah. Then stayed a while at 3.15v. Discharged to 2.4v. After decharching voltage moved up to 3.1v.
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Yea, that's about right. There's a lot of extra surface charge when the cells are charged, up to 3.65V. Normal operation is 3.3V. My pack has extra zip when first out the door, but will quickly settle in at normal operating voltage. That is NOT "sag." Discharging down to 2.4V should be considered borderline safe. Most opinion is to stop discharging below 3.0V, but you should be OK down to 2.4V. Get some celllogs on your pack if you plan on rides that take you down to that range. I don't. 20ah is twice what I need on a daily basis, so I never see anything below around 3.2V. Best. :mrgreen:
 
3.65V is fully charged, it is not "surface charge". charging up to 3.3V is not charged.

if you do not charge each cell up to it's full capacity then the pack does not have a chance to balance under the BMS and will become imbalanced and be damaged by over discharge of the low cell. this has happened too often already.
 
If you need a bms and charge to 3.8v and drain to 2.5v on grade B cells. Just to say you get 20ah out of a 18.5ah cell. Do we need to prove this in real live every time. On victpower 18.50 usd. grade B cells ? What for ?
 
i made some valueable experience. due to an inappropriate charching adapter i used little crocodile clamps to do a quick internal resistance measurement. this was a BIG mistake. surface resistance is much to high. i changed that to heavy duty clamps and ir went down to 11mohm. could reduce that even more by adding additional pressure to the clamps. so i'm hapy with it now. seems ir is a bit higher than nominal (like some older cells) but they still can deliver 19.500mah. so no need to open a paypal claim.
now i need to find a way to test them all. 42 cells and 5h for a full test means days of testing. i'm looking for a 2-3c load. but for 3.3v this would be a really small value resistor. :(
 
dnmun said:
3.65V is fully charged, it is not "surface charge". charging up to 3.3V is not charged.

if you do not charge each cell up to it's full capacity then the pack does not have a chance to balance under the BMS and will become imbalanced and be damaged by over discharge of the low cell. this has happened too often already.
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Could balance to 3.4, to allow for tolerances, then sure to be all full.
There's nothing above 3.33ish if there is, there's something wrong.
Why wait for mAh of charge.
If a cell is constantly overdischarging must be a prob.
 
i'm not sure if i fully understand what you mean: you say that the cell should not take any more charge above 3.3v?? this is not what happens here.
cell has 3.3v. i start charging and voltage goes to 3.5v almost immediately. than it takes some time to reach 3.6v. i don't know if this is due to high resistance.
 
There's quite a few charge/discharge curves on the ES.
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=37955&start=150#p566813 for one.
Can see the cells hit the wall at 3.3Vish level and terminal voltage rapidly escalate at this voltage without constant voltage charge and balancing for a few mah of charge.
You find if you rest your pack for a while they will settle to 3.3V level bleeding off the fluff zip mentioned.
 
it really is not fair for you to deliberately misinform him since he doesn't realize you don't know what you are talking about.

using terms like 'fluff' and 'surface charge' as though they mean anything at all. shame on you.

3.65V is charged. period. 3.3V is not charged. period.
 
dnmun said:
it really is not fair for you to deliberately misinform him since he doesn't realize you don't know what you are talking about.

using terms like 'fluff' and 'surface charge' as though they mean anything at all. shame on you.

3.65V is charged. period. 3.3V is not charged. period.
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Agreed. This is why manufacturers of lithium cells list e.g. 80% DOD - 2000 cycles, 50% DOD - 3000 cycles etc. from fully charged cell and not some odd 3.4V. Cell could have 10AH at 3.3V as well as 16AH at the same voltage.
Not charging your cell does not equal taking care of it!
 
So at 3.4V what level is a cell at compared to 3.65?
 
agniusm said:
dnmun said:
it really is not fair for you to deliberately misinform him since he doesn't realize you don't know what you are talking about.

using terms like 'fluff' and 'surface charge' as though they mean anything at all. shame on you.

3.65V is charged. period. 3.3V is not charged. period.
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Agreed. This is why manufacturers of lithium cells list e.g. 80% DOD - 2000 cycles, 50% DOD - 3000 cycles etc. from fully charged cell and not some odd 3.4V. Cell could have 10AH at 3.3V as well as 16AH at the same voltage.
Not charging your cell does not equal taking care of it!
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Not lifepo4 generally, A123 pouch cells. Also your mentioning DOD as if its relavent here, its not, charged to 3.4 it will live longer with same %DOD.
 
dnmun said:
it really is not fair for you to deliberately misinform him since he doesn't realize you don't know what you are talking about.

using terms like 'fluff' and 'surface charge' as though they mean anything at all. shame on you.

3.65V is charged. period. 3.3V is not charged. period.
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I don't know you, I don't know why you would want to get off on saying 'deliberately misinform' as if I'm being malicious about discussing battery charging, :? weird.
Prove the science, you havnt yet.
 
I know measured six cells and they are all above 19ah. This is great. Internal resistance is somewhere in the low 10s. Do you think this still OK?
Any idea how I can discharge them at 30a? I calculated resistor for that and came to 0.2 ohm. Can't find any resistor that low with 100w+.
 
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